b is the increase in weight of the calcium chloride tube.
12 x a x 100
44 x w
2 x b x IPO
=' per cent, of carbon.
= per cent, of hydrogen.
Example. — 0*1510 gram of oxalic acid gave 0*1055 gram of
CO2 and o-o68 gram of H2O.
I2X020S52LIOO = 0 cent of carbon.
= 5-00 per cent, of hydrogen.
J r &
Calculated for C2H6Oa : C — 19 '04 per cent. ; H = 476 per
As a rule, the carbon is a little too low through loss of mois-
ture from the potash apparatus, whilst the hydrogen is too high,
probably through incomplete drying of the air and oxygen from
the gas-holders. The discrepancy should not exceed 0*2 per
cent, of the theoretical amount. If the substance burns with
difficulty it should be mixed with fine copper oxide in the
manner described under quantitative estimation of nitrogen.
The Combustion of Volatile and Hygroscopic Sub-
stances. — If the substance is a non-volatile liquid it may be
weighed in a boat like a solid ; if it is hygroscopic the boat
must be enclosed and weighed in a stoppered tube. If it is a
volatile liquid a glass bulb or tube, drawn out into a neck as
shown in Fig. 11, must be used. The
bulb is first weighed, and the liquid
is introduced by warming the bulb
gently to expand the air and then FIG n.
inverting the open neck under the
liquid. The operation may require repeating. The tube is then
sealed and weighed again. Before introducing the bulb into
the tube the neck is nicked with a file and broken off. It
is then placed in the boat and pushed into the combustion
tube. In the combustion of a substance like naphthalene, which
is moderately volatile, the greater part is vaporised by the
heat of j;he copper oxide spiral in' contact with the boat. The